At present, there is an increased demand for the cleanliness of storage tanks and other containers storing goods such as fuel oil, fish oil and beverages of various types e.g. beer, soda-drinks or milk. The apparatus commercially available for cleaning storage tanks place considerable requirements to the type of space to be washed and cleaned. In the case of storage tanks, the size, position of openings and the presence of columns inside the tank can limit the utility of the apparatus. In many cases, apparatus specific for certain kinds of tanks have to be constructed. In most cases the apparatus operate at high pressure thus making them expensive and bulky. Furthermore, the high pressure involved increases the the risk of explosion in the case of tanks storing explosive and/or inflammable materials.